Código SQL [-] update RDB$RELATION_FIELDS set RDB$NULL_FLAG = 1 where (RDB$FIELD_NAME = 'TUCAMPO') and (RDB$RELATION_NAME = 'TUTABLA')
update RDB$RELATION_FIELDS set RDB$NULL_FLAG = 1 where (RDB$FIELD_NAME = 'TUCAMPO') and (RDB$RELATION_NAME = 'TUTABLA')